pci_bus_for_each_resource, transparent bridges and rsrc_nonstatic.c

[Bjorn Helgaas]

On Monday 22 March 2010 02:21:35 pm Dominik Brodowski wrote:
> Hey,
> 
> On Mon, Mar 22, 2010 at 01:08:35PM -0700, Bjorn Helgaas wrote:
> > > So, what should we do? 
> > 
> > Let's back up a bit.  I don't know enough about PCMCIA, and I don't
> > see the problem yet.  We have the 00:1e.0 bridge leading to bus 04,
> > and 04:06.0 is a CardBus bridge.  These three windows are the ranges
> > positively decoded and forwarded by the 00:1e.0 bridge:
> > 
> >   yenta_cardbus 0000:04:06.0: pcmcia: parent PCI bridge I/O window: 0x1000 - 0x1fff
> >   yenta_cardbus 0000:04:06.0: pcmcia: parent PCI bridge Memory window: 0xd2000000 - 0xd40fffff
> >   yenta_cardbus 0000:04:06.0: pcmcia: parent PCI bridge Memory window: 0xd0000000 - 0xd1ffffff
> > 
> > But the bridge is in subtractive-decode mode, so it *also* forwards
> > anything it sees that is unclaimed by other devices on bus 00, which
> > means the 04:06.0 CardBus bridge will also see these ranges:
> > 
> >   yenta_cardbus 0000:04:06.0: pcmcia: parent PCI bridge I/O window: 0x0 - 0xcf7
> >   yenta_cardbus 0000:04:06.0: pcmcia: parent PCI bridge I/O window: 0xd00 - 0xffff
> >   yenta_cardbus 0000:04:06.0: pcmcia: parent PCI bridge Memory window: 0xa0000 - 0xbffff
> >   yenta_cardbus 0000:04:06.0: pcmcia: parent PCI bridge Memory window: 0xc0000000 - 0xfebfffff
> > 
> > Why do you care whether these additional ranges are excluded?  They
> > should be just as usable as the first three.
> 
> Quoting rsrc_nonstatic.c:
> 
>         /* If this is the root bus, the risk of hitting
>          * some strange system devices which aren't protected
>          * by either ACPI resource tables or properly requested
>          * resources is too big. [...]
>          */
> 
> Or, as Alan put it -- when it came to I/O resources in the 0x100-0x3ff area:
> 
> 	"Which crashes older thinkpads, some ATI chipset systems and
> 	 usually anything containing an NE2000 clone in ISA space."
> 
> You can still use subtractive-decoded resources, but then you have to add
> them to /etc/pcmcia/config.opts and run pcmcia-startup-bridges (or echo the
> resource to a sysfs file).

It's too bad we still have such manual configuration.  Is there still
information there that we can't figure out automatically?

> Now, "usecrs" is only used on 2008-or-newer systems where we _hope_ that all
> resource "consumers" are accounted for. So the problem might be mitigated.
> However, I wouldn't dare to use ioports 0x0-0xff anyways for they usually
> are used for onboard legacy devices...

Right.  But PCMCIA is at no greater risk than regular PCI, right?
It looks like both will allocate only above PCIBIOS_MIN_IO (0x1000).

Bjorn